Local Stresses in Metal Matrix Composites Subjected to Thermal and Mechanical Loading

One of the important damage mechanisms in metal matrix composites is fiber/matrix separation. The interfacial region between the fiber and matrix is typically brittle and relatively weak, and therefore failure in this region may precede failure of the fiber and matrix. An elasticity solution has been used to analyze matrix stresses near the fiber/matrix interface in continuous fiber reinforced metal matrix composites. This micromechanics model consists of a cylindrical fiber and cylindrical sheath of matrix embedded in an orthotropic media representing the composite. The micromechanics model is used to predict thermal and mechanical properties for a lamina. These properties are then used in a laminate analysis to determine ply level stresses caused by a thermomechanical loading of the laminate. Finally, for a given ply, the ply level stresses and thermal loading are used in the micromechanics model in order to predict local stresses near the fiber/matrix interface.

Predictions from the closed form micromechanics model, which assumes cylindrical symmetry, have been compared to predictions from a finite-element model in which the fibers are arranged in a square array. Near the interface, stresses predicted by both models are in reasonable agreement. The micromechanics model was also used to predict the onset of fiber/matrix separation. Model predictions for a variety of laminates were in reasonable agreement with experimental data.